Build your own CD battery tab welder for about $100.00+-

[FastDemise]

I'm starting up my own little welder now. Just curious how much capacitance do I really need? I am getting (.8F) 8x of these http://www.digikey.com/product-search/e ... 104U016X5C getting a 1000v 200a SCR. As far as weld leads go was just curious how people connected their thick cables from the caps to the weld leads. Just gonna try and use some thick copper bar and wondering how I am going to attach my 8 or 4ga wire to it.

[texaspyro]

Just curious how much capacitance do I really need? I am getting (.8F) 8x of these http://www.digikey.com/product-search/e ... 104U016X5C getting a 1000v 200a SCR.

Why pay $400+ for those caps when a Rockford/Monster Cable/Scosche cap can be had for $50 or so and will probably work better?

To do serious welds you will need around 3F. And that SCR will be vaporized.

[texaspyro]

A very good read about the development and issues of doing a welder:

http://www.turtlesarehere.com/html/cd_welder.html

[FastDemise]

Just curious how much capacitance do I really need? I am getting (.8F) 8x of these http://www.digikey.com/product-search/e ... 104U016X5C getting a 1000v 200a SCR.

Why pay $400+ for those caps when a Rockford/Monster Cable/Scosche cap can be had for $50 or so and will probably work better?

To do serious welds you will need around 3F. And that SCR will be vaporized.

I was able to get them for $12 a piece. Though I do see how quality audio caps might be cheaper. When you say quality welds I only need to weld the aluminum A123 batteries to nickel strip. Won't need to be more robust than needed. If I need 3F just for that I'll rethink my setup. So one of those 'hockey puck' scr might be needed.

*Added*
With each caps being 7 mOhm having 8 in parallel drops my cap resistance to something like .875mOhm (12kA @ 12v) if my math is right. Wouldn't that be low enough that I can use less capacity warranted I get a SCR that's beast enough.

[texaspyro]

It all depends upon the thickness of the tabs that you are welding. I think Mighty Volt needed 3F/18V to get decent welds onto A123 cells with his (10 mil?) tabs. If you are welding 3 mil foil, 1F/12V might do.

[FastDemise]

I have 5mil thick so it maybe possible.....


*Added*
So my SCR is rated at 1600v 200a = 320kW
Using the 320kW but at 16v that's 20,000A it should be able to handle?? With the math showing the low resistance of the caps able to push 12,000A. Am I wrong in thinking the SCR I have will work on paper or am I just using ohms law all wrong?

[amberwolf]

So my SCR is rated at 1600v 200a = 320kW
Using the 320kW but at 16v that's 20,000A it should be able to handle?? With the math showing the low resistance of the caps able to push 12,000A. Am I wrong in thinking the SCR I have will work on paper or am I just using ohms law all wrong?

You already answered your own question: The SCR is rated 200A. You need 100 times that current.

POOF.

(realistically it depends on lenght of pulse, various SCR specs, etc., but just remember that once you start the pulse going, you aren't going to be able to stop it, so if your caps are larger the pulse will be longer, and the SCR has to handle the high current longer. Probably still POOF).

[zakipu]

Unfortunately SCRs are rated for current and voltage not power. The 200A rating is what it can handle continuously at any voltage. The peak current rating should be around 6-7000A, so the SCR should survive depending on the total resistance of the setup and the voltage. Also, hockey puck SCRs are notoriously hard to connect to.

My SCR is rated 14,500A peak, 425A continuous. Datasheet. I have 8 more on the way. PM me if you're interested.

I have about 2.9F from three car caps. Monster: 1.1F, Scosche: 1.0F, and Rockford Punch: 0.8F. Those are just preliminary numbers using a 10 ohm resistor and voltmeter. I'll have better numbers when I get my charge controller up and going. I'm going to use copper bar to connect the caps and SCR then about 2 feet of 1/0 welding cable to the electrodes to keep the total system resistance as low as possible so the most amount of energy goes into the weld. I'll post a schematic and pictures when I get a chance.

[FastDemise]

CD welder.jpg (22.28 KiB) Viewed 864 times

I just replaced using a resistor with a small 15w DC-DC convertor I got from Lyen to adjust the trigger voltage just right. Just waiting on the SCR so I can start making sparks. I'll start off small with just .4F of capacitance and see what I get and test my wiring setup. Then just keep stepping it up until my welds are good.

[malcav]

I'll start with I am sorry i did not read the whole thread so my Q may have been answered. But what is the best type of cap to use? Like aluminum or ceramic?

[Kin]

I'll start with I am sorry i did not read the whole thread so my Q may have been answered. But what is the best type of cap to use? Like aluminum or ceramic?

I've never seen a 1 farad ceramic cap... I think you'll need alu electrolytic caps. In the last 4 pages (i.e, from this page, somewhere in the four previous pages), texaspyro links to where in the thread he describes the good brands of car audio caps. They will be good caps to use.

[pwbset]

Had a weak 1s10p string in my battery pack so de-duct taped the whole pack and found quite a few tab welds had popped apart. Meh. Current setup is identical to the first post in this thread, which is borderline I guess. So last night I ordered a Scosche ECAP1 to go parallel with my old Volfenhag at 16.2v. Hopefully that will get me some deeper welds. Going to re-grind my copper contacts for finer points also so that should help a bit too. Love this tab welding stuff, but need more power!

[texaspyro]

Finer/sharper points are not necessarily better points. They can give tiny weld spots and current densities that are too high and blow out the weld point. And flat points are a no-no... you will never get the electrodes square to the material, yielding the same problem as sharp points. Nice rounded tips work best. The diameter of the point is best determined by trial and error and sparky smoke.

[pwbset]

Nice rounded tips work best. The diameter of the point is best determined by trial and error and sparky smoke.

Good advice. Much appreciated, thank you.

[The Mighty Volt]

Finer/sharper points are not necessarily better points. They can give tiny weld spots and current densities that are too high and blow out the weld point. And flat points are a no-no... you will never get the electrodes square to the material, yielding the same problem as sharp points. Nice rounded tips work best. The diameter of the point is best determined by trial and error and sparky smoke.

What I do is I push my blunt but rounded tips, {sort of like a pencil whose tip has worn down}, into the tab, making an indentation.

Then I lift the electrodes off and then gently nestle them back into the same indentations.

I apply a small amount of pressure, and fire.

Works great everytime. The indentations cup the electrodes and catch more of the discharge, making for a better weld.

[boppinbob]

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[The Mighty Volt]

It all depends upon the thickness of the tabs that you are welding. I think Mighty Volt needed 3F/18V to get decent welds onto A123 cells with his (10 mil?) tabs. If you are welding 3 mil foil, 1F/12V might do.

Hi Texas...yes...that was in the early days but those welds were being used to do the DeWalt nickel. I can do quality welds now with properly-blunted terminals onto the thin stuff {.02 I think} with around 15v.

12v will do it, for instance if you are tabbing a cell just to charge it and discharge it and testing purposes.

15v is better for the final weld.

Today, on 15v, I put two pieces of nickel down on each other, on a wooden work bench, and burned right through to the wood as I had a dirty hot positive electrode.

Thinking of building me one of those Fritz-Welders that you have...what do I need, where can I get it, to make one?

Cheers fella.

[texaspyro]

Fritz is (was) selling boards again: http://frikkieg.blogspot.com/

[hillzofvalp]

Hi, guys. A while back I posted a welder project with 3 .3F Spraque powerlytic caps. I gave up after a bug in my circuit. The good news is I reconstructed the welder and got it working.

Here is the good: I can blow holes in 5mil nickel on A123 26650s, dual pulse is working, and SOMETIMES I get a good weld.

The bad: when I have a good weld, the battery sticks to the copper electrodes, often leaving a smidgen of copper on the nickel. Most of the time the weld blows out and pops, leaving a little splatter/crater of nickel and blackness.. I can't find a good setting. I have been trying 300-600microsecond first pulses, 30-90millisecond pulse width, and 600-1200 Microsecond pulses. This is all at initial voltage of 15V (ending as low as 8-9V).

My theory is it has something to do with electrode contact. My electrodes are reworked sunstone double sided electrodes spaced at around .14 C-C and .065" in diameter. I file them even, weld, then one or the other wears faster (I understand that is common.

Any advice?

Update: after an hour of tinkering, I found that the positive needs to be like .005-.015" longer than the negative. I also made the structure more rigid for more consistent weld pressure. I also have it tuned in currently to 230microseconds first pulse, 20milliseconds width, and 1280microseconds second pulse. This is all at about 13.4V (using 4S A123 pack for instant cap recharges). Better results, but the welds aren't quite strong enough. I may try a bigger power supply to auto charge to 15V or maybe try a smaller initial pulse.

[texaspyro]

I think that your pulses are way to short...

[hillzofvalp]

K. Care to elaborate? What do you recommend for the ratio between pulses and the width? I'm having better luck right now at 440 microseconds first pulse and 2000 microseconds second pulse. You want the first pulse to be say around 800 microseconds and the second pulse to be like 3000 microseconds?

BTW I just obtained a 20V 1F monster cap to try.. didn't you say these were the best?

[hillzofvalp]

I have 8 3703 FEts capable of something like 1000A bursts each. Assuming 6500A is the max safe current for FEts that may or may not be closely matched, how would u calculate the corresponding voltage and pulse lengths for the monster cap?

Is it safe to assume that. The FETs will be okay say at 7000-7500A since they appear to fire at the same time at 2000-3500A currently?

[texaspyro]

K. Care to elaborate? What do you recommend for the ratio between pulses and the width? I'm having better luck right now at 440 microseconds first pulse and 2000 microseconds second pulse. You want the first pulse to be say around 800 microseconds and the second pulse to be like 3000 microseconds?

BTW I just obtained a 20V 1F monster cap to try.. didn't you say these were the best?

I seldom weld by time anymore. My welder lets you specify the energy to put into the pulses. This helps compensate for things like inconsistent connections. As a general rule you start doing single pulses of increasing energy until the material starts sticking and then back off some. Set the delay to the main pulse to the length of the first pulse, and the time/energy of the main pulse to 4-5 times the first pulse.

Monster Cable and Rockford 1F caps work very well. Avoid the Rockford 2F and larger caps... they are "hybrid" caps that don't work for welding.

[hillzofvalp]

Now that I've gotten into it I kinda want to just specify the energy rather than the pulse lengths. How do you determine first pulse? Is that a separate setting on your welder, but in energy?


How would u recommend sampling the actual current? A shunt (such as a known length of the welding cable)? Or do you just do .5cv^2 sampling with known capacitance values?

[The Mighty Volt]

has anybody got one of these yet so that they can satisfactorily weld copper sheet?